Study on the properties of TiC, Nano-CaCO3, and steel fiber reinforced concrete based on RSM-BBD: optimization of mechanical properties.

Abstract

As modern civil engineering demands increasingly higher strength, toughness, and long-term stability from concrete materials, the performance limitations of ordinary concrete in complex service environments have become increasingly apparent. The dual-blending modification of nanomaterials and steel fibers (SF) has emerged as an effective technical approach to overcome these limitations. The ratio design of the TiC-NC-SF dual-blending system has largely relied on empirical methods, lacking systematic quantitative optimization. The synergistic mechanisms among multiple factors remain unclear, hindering the engineering application of modified concrete. This study employs Box-Behnken experimental design and response surface methodology to systematically investigate the influence patterns of three factors on concrete's 28-day compressive strength, splitting tensile strength, and flexural strength. Scanning electron microscopy (SEM) characterization reveals microstructural mechanisms, while model optimization validates optimal ratios. Results indicate the dominance order of the three factors on concrete mechanical properties is SF > NC > TiC (with NC and TiC having similar effects on compressive strength). A significant synergistic enhancement effect exists between TiC and NC (interaction term P < 0.05). Both TiC and NC enhance concrete strength by optimizing matrix density through "hydration regulation and multi-level filling," while SF dominates crack control via "bridging crack propagation and energy dissipation toughening." No significant interaction was observed between TiC-SF or NC-SF (P > 0.05). Concrete compressive strength exhibits a quadratic variation with increasing dosage of all three factors, with SF exerting greater influence on splitting tensile strength and flexural strength. The response surface model optimization yielded the optimal mix design of TiC 2.12%, NC 2.14%, and SF 1.19%. Its 28-day compressive strength, splitting strength, and flexural strength reached 69.83 MPa, 7.22 MPa, and 9.34 MPa, respectively (measured values). The response surface optimization values were 70.50 MPa, 7.52 MPa, and 9.60 MPa, respectively. According to the experimental results, these values increased by 22.66%, 26.44%, and 15.02%, respectively, compared with the control group (CG). The performance deviation from the optimal experimental group was less than 0.5%, and the deviation from the optimization target was within 10%. SEM characterization revealed that the cement matrix in the CN10 and CN18 groups exhibited significantly higher densification than the CG group, with SF tightly bonded to the matrix interface.